1. Field of the Present Invention
The present invention relates to maintenance of connectivity between a mobile node and other nodes involved in a movement of the mobile node in a mobile network environment.
2. Description of the Related Art
In recent years, researches have been conducted on a mobile IP, which is a technique for allowing a moving terminal to maintain IP communication regardless of a position of the terminal. Recently, there have been many cases where companies and organizations carry out demonstration tests, and provides the service through hot spots and the like. Standardization of the mobile IP has already been promoted in the field of IPv4. At present, standardization organizations such as the IETF have actively discussed to realize the mobile IP based on IPv6.
However, a mobile IP function is not implemented in all IP devices. It is expected that a chip mounted with a simplified IP stack having a minimum IP function will be implemented in small-sized portable terminals, devices that do not perform IP communication frequently, and the like. Also, there are some of the devices currently used that will not have the mobile IP function additionally implemented.
In such cases, only with the implementation of the mobile IP function that is currently discussed in the standardization organizations, a node not supporting the mobile IP function and a mobile node supporting the mobile IP function cannot communicate with each other in some cases Thus, means for solving this problem is required.
There is a mobile IP technique as a technique taking into account convenience at the time when an IP node moves from one segment to which the IP node belongs to another. As the mobile IP technique, those for IPv4 and IPv6 have been laid open to public, and respectively defined in RFC2002, draft-ietf-mobileip-vipv6, and the like.
In addition, several patents have been laid open to the public in order to supplement these techniques.
For example, there is disclosed a technique concerning speed-up of packet transfer path switching following movement and optimization of a redundant path for packet transfer following movement, while taking into account compatibility to IP of mobile communication networks (TOKUKAI 2002-185520).
This laid-open patent application discloses a technique for allowing, by using the techniques described above, a MN to perform packet transmission and reception without changing information of the MN's own node when the MN moves from one segment to another. In addition, it is also possible to move from one link to another without suspending communication.
However, these are techniques assuming communication between nodes compatible to the mobile IP function or communication using a “home address (hereinafter, HoA)” of the MN.
In the conventional techniques, as shown in FIG. 15, when a CN sends a connection request to a MN and the CN and the MN communicate with each other using an HoA of the MN, communication is never interrupted following movement of the MN. However, as shown in FIG. 16, in a case where a MN located in a foreign segment sends a connection request to a CN, since the CN, which is a node not supporting the mobile IP function, cannot recognize an HoA Option (hereinafter, HoAOP), the CN starts communication using a Care of Address (hereinafter also referred to as CoA) of the MN. After this connection is established, a destination of a packet to be sent from the CN to the MN is changed to an old CoA of the MN, following segment movement of the MN. Thus, the packet does not reach the MN after the movement and the communication is interrupted.
In general, a MN having a contract with a mobile communication carrier, an ISP, or the like, has a home segment in a segment inside the carrier or the ISP, and the MN never returns to the home segment. When an IP network is established, it is unlikely that the mobile IP function is applicable to all nodes, and may not be applicable to devices mounted with a simplified stack or the like.
Therefore, in daily use, a connection request from a MN to a node not supporting the mobile IP function is communicated using a CoA. As a result, the communication is interrupted following movement of the MN.
For example, in a case where a cellular phone currently used widely is adapted to the IP, when a user attempts to receive music, video, or the like, reception cannot be continued unless a server supports the mobile IP function. As a result, a service cannot be provided.